Objective. - Our aim was to evaluate cardiac function and myocardial contractility in patients with overt hypothyroidism using two-dimensional speckle tracking echocardiography (2D-STE) strain imaging and real-time three-dimensional echocardiography (RT3DE) and compare the changes at one month after starting the treatment. We also compared the P wave dispersion (Pdis) in patients with and without hypothyroidism. Subjects and methods. - Forty-one patients with overt hypothyroidism and forty age- and body mass index-matched healthy subjects underwent conventional echocardiography, RT3DE and 2D-STE for assessment of resting LV function. Electrocardiography (ECG) recordings were obtained and the P wave parameters were calculated. Measurements of RT3DE volumes and ejection fraction (EF) were performed. Global longitudinal strain (GLS) was calculated from 3 standard apical views using 2D-STE. Results. - Patients with overt hypothyroidism had significantly longer isovolumic contraction time (P < 0.001), deceleration time (P < 0.001) and isovolumic relaxation time (P <0.001). On RT3DE evaluation, none of the patients in both groups had LV systolic dysfunction with comparable LVEF and LV volumes. However, speckle tracking analysis showed that GLS was significantly reduced in the overt hypothyroidism group compared to control group (P <0.001). At one month follow-up after the treatment, GLS significantly improved in overt hypothyroidism group (P <0.001). Patients in the overt hypothyroidism group had increased Pdis compared to control group (P = 0.02). Conclusions. - Overt hypothyroidism may be related to impairment of LV longitudinal myocardial function, and 2D-STE is useful for the detection of early impairment. Successful treatment of overt hypothyroidism has a beneficial effect on cardiac functions. In addition, overt hypothyroidism has increased risk for atrial arrhythmias due to high Pdis value. (C) 2013 Elsevier Masson SAS. All rights reserved.